1. Field
This invention pertains to the field of voltage controlled oscillators (VCOs), and more particularly to an integrated standing wave VCO.
2. Description
The continuous growth of broadband data communications has resulted in the opening of V-band and even E-band for terrestrial wireless applications. In transceiver systems, the voltage-controlled oscillator (VCO) is a key component. It provides the required local reference signal for frequency translation. For the system-on-a-chip realization of wireless transceivers, fully integrated VCO circuits are in high demand, since they provide easy and flexible integration with more reliable performance. But at millimeter wave frequencies, designing such circuits is a big challenge because it requires low-parasitic, high-quality passive devices and active devices to achieve acceptable tuning range and phase noise levels. Fortunately, modern complementary metal oxide semiconductor (CMOS) technology has pushed the cut-off and maximum frequencies of active CMOS devices beyond 100 GHz, and implementing integrated VCOs at such high frequencies has become feasible. In the past few years, great efforts have been made in this domain, with a focus on reducing the phase noise and increasing the frequency tuning range.
In the VHF, UHF, and low GHz microwave frequency bands, many VCOs employ an on-chip lump spiral inductor as the inductive component in the LC tank. However; in the higher microwave and millimeter wave bands, this type of inductor suffers from serious substrate losses. This prevents the VCO from achieving low phase noise and wide tuning range.
Accordingly, it would be advantageous to provide an integrated oscillator at microwave and millimeter wave frequencies that can provide good phase noise performance. It would further be desirable to provide an integrated VCO at microwave and millimeter wave frequencies that can provide good phase noise performance and a wide tuning range.
The present invention comprises an integrated standing-wave voltage controlled oscillator with a dual-mode coplanar waveguide resonator.
In one aspect of the invention, a voltage controlled oscillator (VCO) is provided that is integrated with a semiconductor substrate. The VCO comprises: a pair of oscillator transistors and a resonant circuit. The oscillator transistors each have a control terminal and an output terminal. The oscillator transistors are cross-coupled to each other such that an output of each oscillator transistor is coupled to an input of the other oscillator transistor. The resonant circuit is connected between the control terminals of the pair of oscillator transistors. The resonant circuit comprises a dual-mode coplanar waveguide resonator and first and second varactors each having a first end thereof connected to a tuning voltage input and having a second end connected to the control terminal of a corresponding one of the oscillator transistors. The dual-mode coplanar waveguide resonator comprises: an electrically conductive common line extending lengthwise in a first direction and connected to a first supply voltage for the oscillator transistors; and at least first through fifth electrically conductive lines sequentially arranged lengthwise substantially in parallel with each other in a second direction which is substantially perpendicular to the electrically conductive common line. The electrically conductive common line and the first through fifth linear electrically conductive lines are all arranged at a first level with respect to the semiconductor substrate. Each of the first through fifth linear electrically conductive lines has a first end and a second end opposite the first end. The first ends of the first through fifth electrically conductive lines are all connected to the electrically conductive common line; the second ends of the second and fourth electrically conductive lines are each connected to the output terminal of a corresponding one of the oscillator transistors; and the second ends of the first, third, and fifth electrically conductive lines are floating.
In another aspect of the invention, a voltage controlled oscillator (VCO) comprises a cross-coupled differential transistor pair having a pair of input terminals and a pair of output terminals; and a resonant circuit coupled to the input terminals of the cross-coupled differential transistor pair. The resonant circuit comprises: a pair of voltage-dependent capacitive elements and a pair of inductive elements. Each voltage-dependent capacitive element is connected between a corresponding one of the output terminals of the cross-coupled differential transistor pair and a control voltage terminal. Each inductive element is connected between a first supply voltage and a corresponding one of the output terminals of the cross-coupled differential transistor pair. Each inductive element comprises a coplanar waveguide. Each coplanar waveguide includes: a central signal line and a pair of coplanar waveguide (CPW) ground lines disposed on either side of the central signal line. Each signal line is connected at a first end to the first supply voltage and at a second end to the corresponding one of the output terminals of the cross-coupled differential transistor pair. Each of the CPW ground lines is connected at one end to the first supply voltage and is floating at the other end.
In yet another aspect of the invention, a standing wave oscillator comprises: a cross-coupled differential transistor pair having a pair of input terminals and a pair of output terminals; and a resonant circuit coupled to the input terminals of the cross-coupled differential transistor pair. The resonant circuit comprises: a capacitance between the input terminals of the cross-coupled differential transistor pair; and a differential dual-mode coplanar waveguide (CPW) having opposite differential ends thereof connected to respective input terminals of the cross-coupled differential transistor pair, wherein CPW ground lines of the differential dual-mode coplanar waveguide each have a first end thereof connected to a first supply voltage and have a second end thereof floating or unterminated.